IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 3, JULY2004 1225 The Capacitive Coupling Between EHV Lines and Nearby Pipelines Mohamed M. Saied, Senior Member, IEEE Abstract—This paper addresses the effect of the electrostatic field due to extra high voltage (EHV) overhead transmission lines on pipelines in the vicinity of those power lines. Two measures for this effect are used: the maximum electric field on the pipe sur- face and the total electric charge on the pipeline per unit length. A mathematical model is presented for assessing these two mea- sures. The results of applying the model to a situation involving a single-circuit, six-bundle, three-phase, 750-kV EHV line with flat conductor configuration are presented and discussed. The first set of results refers to a parallel pipeline of radius 0.5 m. The depen- dence of both the maximum electric field (at the top of the pipe) and the charge per meter on the distance between the pipeline and the tower center is similar to the distribution of the electric field beneath the tower at the ground surface. It shows maxima of both quantities if the pipe is exactly under one of the outer phases of the power line. At a distance of about 35 m from the tower center, both the electric field and the charge per unit length drop to 50% of their maximum values. The electric field is found to increase almost linearly with the clearance between the pipeline and the ground surface. The charge changes in a more complicated way with the clearance. It decreases if the pipe clearance increases from 0 to 0.2 m, then increases steadily beyond this value. For a given distance from the 750-kV line and for a fixed clearance from the ground, both the electric field and the electric charge per unit length on the pipeline will increase with the pipe radius. This paper will deal also with the impact of the pipeline on the nearby EHV power line and its associated network. The results will show that for a solidly earthed power network, the presence of the pipeline will be accompanied by a slight increase in the neutral cur- rent. On the other hand, for a power network with an inductively earthed neutral, there will be a tendency toward a parallel reso- nance that can occur for particular values of the neutral induc- tance and pipe radius. This resonance will result in an increase in the system’s neutral potential, which will be primarily limited by the network losses. Index Terms—Capacitive coupling, electrostatic interference, extra high voltage (EHV) lines, pipelines. I. INTRODUCTION T HE ever increasing cost for right of ways suitable for erecting extra high voltage (EHV) power lines and pipelines as well as the noticeable current public awareness toward the visual and environmental impact of those lines have led to exploring the possibility of using the close or even common corridors for both power and pipelines. This, of course, reduces the land cost considerably. Neverthe- less, several technical problems will arise from the close prox- imity of those lines. One of those problems is the issue of inter- ference between the power and pipelines, during normal opera- Manuscript received March 6, 2003. The author is with the Electrical Engineering Department, Kuwait University, Safat 13060, Kuwait (e-mail: saied@eng.kuniv.edu.kw). Digital Object Identifier 10.1109/TPWRD.2003.823211 tion as well as in emergency conditions [1]–[5], [8]. If we focus on the possible concerns regarding the effect of power lines on nearby pipelines, the electromagnetic coupling represents one of the possible reasons for endangering the personnel and equip- ment dealing with the pipelines. Basically, it has two compo- nents: inductive and capacitive. The first one is due to the mag- netic field generated by the currents in the power line. Since this effect is proportional to the line currents, steady-state magnetic coupling can assume dangerous values especially during fault conditions. The objective of [1], which is one of two volumes jointly issued by the Electric Power Research Institute (EPRI) and the Pipeline Research Committee (PRC) of the American Gas Association (A.G.A), was threefold: documenting available data on mutual interaction between electric power lines and par- allel natural gas pipelines, procedures for evaluating the power frequency voltages and currents electromagnetically induced on the gas pipelines, and procedures to reduce these effects on both components and personnel. Reference [2] reports on a study dealing with a 525-kV power line, railroad, and pipeline sharing a common corridor for an exposure length of about 62 mi. Pri- mary concern was given to both the magnetic induction due to current in the transmission line conductors (during normal and faulty conditions) and the electrostatic induction due to voltage on these conductors. The impact on the safety considerations for railroad and pipeline operation or maintenance personnel as well as on the compatible operation of electrical and electronic equipment associated with the pipeline and railroad system were discussed. Two main criteria were suggested: the magnetically induced voltage to earth on an individual conductor, or the ac- cessible voltage difference between two conductors at an equip- ment location was limited to 60 V [5], and the electrostatically induced available short circuit current to earth from a conductor was limited to 6 mA. In [3] and [4], a study specializing in the areas of inductive and conductive coupling between power lines and natural gas pipelines was presented. A computer package, called ECCAPP, was described. Its problem-solving abilities and applications are demonstrated. This paper summarizes also some of the results of parametric analysis examining the role of various factors affecting the electrical interference levels caused in pipelines by nearby transmission lines under fault conditions. Reference [8] acknowledges that the problem of ac interference has been known for more than 30 years, and discusses the three types of interference between ac lines and nearby pipelines: electro- static capacitive, resistive ohmic, and electromagnetic inductive interference. With regard to the capacitive component, the sig- nificance of grounding welded pipe sections lengths exceeding a few hundred to 1000 ft is discussed. It is further stated that with practical pipe coating, this type of coupling is of minor signifi- cance after construction. 0885-8977/04$20.00 © 2004 IEEE